[clairity]

i wish this were more common knowledge. narrowing lanes is among the best ways to slow cars down, if that's the goal.

but in many cases, that goal is missapplied to reduce accidents. accidents are typically not caused by speed, but rather distraction or anger. it hard to enforce attention and mindfulness, so we regulate speed as a (poor) proxy (partially for harm reduction, as speed increases severity of accidents), which directly leads people to wrongly associate speed as the cause of accidents.

it makes sense, for example, to reduce vehicle speeds around schools to reduce harm in case of accidents with small people. but rather than an artificial speed limit that depends on police enforcement, narrow the lanes to 8 feet and people will naturally drive 15-20 mph in those school zones without the added enforcement burden (and use the remaining road space for bike lanes).

[emj]

Lower speed leads to fewer deaths; at ~18 mph almost no one dies, compared to 80% of pedestrians who are hit at 30 mph die. Your reasoning comes from another angle it might be correct but you can never assume people are attentive in traffic, neither pedestrians nor drivers, that's why you need rules and infrastructure that makes it possible to share the roads.